One example of the conventional image direction determining device is described in Patent document 1. The technique described in the Patent document 1 is a technique of incorporating a slant detector into an electronic camera, and determining an up-and-down direction of an image by acquiring a slant of the camera at the time of capturing the image. As a configuration for this technique, the image direction determining device includes an electronic image acquiring device for acquiring an image, a rotation detector for detecting the rotation of the image acquiring device within a plane that is vertically rotated and generating a rotation output value that is almost equal to a 90 degree integer multiple from a reference position where the image acquiring device is located at a horizontal position, and a signal processor for generating a processed digital image signal based upon the rotation output value.
Further, one example of another image direction determining device is described in Patent document 2. The technique described in the Patent document 2 is a technique of detecting a human face from an input image and determining an up-and-down direction of the face as an up-and-down direction of the image. FIG. 19 is a block diagram illustrating a configuration example of the conventional image direction determining device described in the Patent document 2 etc. As shown in FIG. 19, the image direction determining device for determining an up-and-down direction of the image by employing an up-and-down direction of the face includes a camera image picking-up section 91 for capturing an image and outputting an image, a digital image signal processing section 92 for compressing the image, a storing section 93 for recording the compressed image, and a face recognizing/image processing section 95 for detecting a human face appearing on a subject image, determining the up-and-down direction of the face, and when a result of the determination demonstrates that the up-and-down direction of the face differs from that of the image, giving an instruction for rotating the image so that the up-and-down direction of the face and that of the image coincide with each other.
Further, in Patent document 3 is described the technique of, with regard to a character image, selecting a recognition candidate character based upon information of the number of the features that are not dependent upon a direction of the character extracted from the character image, rotating a dictionary data associated with the candidate character, and assuming the rotation angle, which is decided according to a degree of the coincidence with the feature data (a relative position of the localized shapes such as a closed-loop of a character, a crossing intersection of a character, a T-intersection of a character, and an endpoint of a character) dependent upon the direction of the character extracted from the character image, to be rotation angle information.    Patent document 1: JP-P1999-225283A (paragraph 0005, FIG. 1)    Patent document 2: JP-P2005-260870A (paragraphs 0012 to 0013)    Patent document 3: JP-P1998-224596A (paragraphs 0010 to 0013)